Verification of practical effectiveness of various applications of electrochemical chloride extractions for cement concrete

Abstract

Maintaining and prolonging the service life of existing reinforced concrete structures are crucial contributions of civil engineer to solve the sustainability issues. Electrochemical chloride extraction (ECE) is one of the maintenance and repair methods to prevent further deterioration of a reinforced concrete structure that is exposes to chloride environments. It arose to answer the question that when the source of corrosion, chloride ions, is extracted or eliminated out the zone around steel reinforcement, it is not clear if the corrosion of reinforcement stops, the passive layer is re-passivated or the deterioration progress could be slowdown. Theoretically, the principle of ECE is similar to cathodic protection since a direct current is applied on reinforced concrete structure in which reinforcing steel is used as cathode and a temporary anode is set up on the surface of concrete. However, the application of the high current or the large quantity of cumulated-applied charge number by using ECE can result the adversities on binding capacity of hydrated cement products or the diffusibility of concrete matrix. Consequently, these adversities would affect the future durability of reinforced concrete structure. Furthermore, while there have been many structures using fly ash and granulated blast furnace slag as mineral admixtures to improve durability of reinforced concrete structure, there are very few studies of ECE on concrete or cement pastes containing them. How to reduce the charge number applied with preserving the efficiency of ECE needs to investigate. Therefore, this research included two objectives.Firstly, the effects of electrical current application thanks to the conduct of ECE on hydrated cement products of cement pastes, especially on C-S-H phase, were investigated. A pair of modified migration cells were used with the applied current density of 4.5 A/m2 and synthesized pore solutions as electrolytes for 8 weeks. Three types of cement pastes with the size of 40 mm by 40 mm by 160 mm were prepared with the water-to-binder ratio of 0.4 including ordinary Portland cement (OPC), fly ash cement (FC) and ground granulated blast furnace slag cement (SC) pastes. After casting, these paste specimens were cured in saturated calcium hydroxide for three months before stopping the hydration process by immersing them into acetone. These pastes were sliced into the size of 40 mm by 40 mm by 5 mm before applying the extraction. Chloride source was supplied by adding 1.5% sodium chloride with respect to mass of binder during mixing cement pastes. After extraction, the acid-soluble and water-soluble chloride contents significantly reduced. Portlandite content increased proportionally with the time of extraction in OPC and FC pastes. Some unsteady gel phases were obtained after a short time the extraction was stopped. Furthermore, the alteration and decomposition of C-S-H were inevitable with different rates depending on the type of cement. The breakage of the chain of calcium silicate hydrate was obtained and the rates…